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    doucment.write(Math.round(2.4));    //四色五入
    doucment.write(Math.random()*10);     //随机数      
    doucment.write(Math.max(10,20,30,40,8500));     //最大值 
    doucment.write(Math.min(10,20,30,40,8500));     //最小值
    doucment.write(Math.abs(-10));                  //绝对值



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